The purpose of this project is to evaluate in a double-blind crossover protocol, the relative safety and side effects of phenobarbital and sodium valproate in children with tonic-clonic seizures. In particular, we are concerned with the effects which these anticonvulsants may have on the behavioral and neuropsychological function of the child. Reviews of the literature indicate conflicting evidence, primarily in adults, about the effect of anticonvulsants upon intelligence, performance, attention and learning or memory. We propose to concentrate on neuropsychologic variables--visual motor performance, attention and learning as they relate to the behavior and academic function of 50 children, ages 6-14, who are placed on these medications for seizure control. Simultaneously we will be evaluating the relative efficacy of these drugs in the control of tonic-clonic seizures. Sodium valproate of phenobarbital will be randomly assigned as the first drug. Prior to the initiation of medication, the neuropsychologic battery of tests will be performed. Routine monitoring of the patient will occur with respect to seizures, side-effects, serum anticonvulsant levels, hematologic and hepatic function. At the end of six months on the initial drug, neuropsychologic tests will be repeated and crossover to the second medication will occur. Monitoring will continue and neuropsychologic testing will be repeated again after 6 months. A small subgroup of this population will also be intensively studied under each drug condition utilizing telemetered electroencephalography. This will be done to provide data regarding the variability of our patients with respect to performance. A final goal of this study is to develop a methodology which will enable clinicians to measure the subtle effects of anticonvulsants on higher cortical function of children. This is necessary to establish the real risk/benefit ratio of anticonvulsants for this population.